1. Field of the Invention
This invention relates to a hammer device in the form of a needle gun including a cylinder housing in which a movable cylinder is mounted in a sliding manner between two compression springs, a floating piston is moved to and from in the cylinder under the influence of compressed air, and delivers a strike impulse to an anvil on which a needle carrier rests under pressure of one of the springs, and several needles in the needle carrier are mounted in an axially sliding manner and under operating pressure bear on the anvil with their needle heads at the end.
2. Discussion of Related Art
Hammer devices are commercially under the description needle guns, and have proven their worth in daily use. Basically, needle guns are used for cleaning surfaces, in order for example to remove old paint remains or rust layers. The manner of operating and the construction of the needle pistols lead to a high material loading. Accordingly, hammer devices of interest can be improved to increase their operating life.
In particular, in order to reduce the wear between the movable cylinder and the cylinder housing, a special sliding seal is known from European Patent Reference EP-A-0 152 376.
A hammer device of the initially mentioned type is likewise known from German Patent Reference DE-U-84 32 499. In this document, the main emphasis is on the extension in the operating life of the needle gun, to address the problem of the wear between the anvil and the cylinder housing.
Then, after the operating life of known hammer devices had remained practically unchanged for years, recently their have been increasing complaints with regard to the known hammer devices for not reaching the usual operating life. Although no changes occurred with regard to design, complaints suddenly appeared. On investigating the devices which were the basis of the complaints, many which had high tension masts were derusted. The investigations revealed that the persons working on the high tension masts were using the hammer device in continuous operation. The continuous operation thereby was accomplished by fixing the actuation button or the trigger lever on the grip of the needle gun with an adhesive tape, so that the needle gun no longer switched off the apparatus on letting go of the needle gun. Thus the worker on the high tension mast practically has only one free hand, and accordingly needs to immediately grab the needle gun and work with it without having to grip around it. For this, the worker has the needle gun fastened for example on a belt on a safety cable.
With usual derusting work, the worker presses the needle gun onto the surface which is to be machined, and thus the needles with their needle heads bear directly on the anvil. When not working, the needles thus hang in the needle carriers and the floating piston is stationary, so that no oscillation of the anvil is effected, and the needles are held in the needle carrier in a non-moved manner.
With the previously mentioned continuous operation with which for example the actuation lever is fastened on the grip with an adhesive tape, the floating piston then moves to and from when one does not work, and as a result of this, the needles do not bear on the anvil. Thus, the floating piston continues to emit its impulses onto the anvil, the oscillation of the anvil is transmitted onto the needle carrier. The needle carrier accordingly also oscillates, which is pressed onto the anvil by the compression spring. The oscillation of the needle carrier causes the needles to oscillate in a practically unloaded manner, and thereby impact onto the anvil which in turn provides the needles with a strike impulse. Accordingly, the needle carrier is loaded in impact by the needle heads. The needle carrier, which is usually manufactured of plastic, is not designed for this type of impact loading and is thus destroyed within a relatively short period.